The invention relates to a device for guiding sheets in a sheet-processing apparatus, particularly, a rotary printing press.
German Published, Non-Prosecuted Patent Application DE 198 29 095 A1 teaches the provision of sheet guiding devices that include an air-permeable guide surface made of porous material at cylinders and drums of rotary printing presses on either side of the printing nip. Diffuse blasted air emerging from the guide surface is intended to facilitate a uniform blasted air emergence. The sheet guiding devices according to DE 198 29 095 A1 are not suitable for smoothing out or pressing wrinkles from a sheet at a large distance in front of the feed nip as the sheet is transported on a sheet guiding cylinder at its front edge by grippers.
It is accordingly an object of the invention to provide a device for guiding sheets in a sheet processing apparatus that overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and that lays out a sheet guiding device having blast nozzles that makes possible a uniform sheet transport on a sheet guiding cylinder.
With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for guiding sheets in a sheet-fed apparatus having a form cylinder, a rubber blanket cylinder, and a sheet guiding cylinder, the sheet guiding cylinder with one of the form cylinder and the rubber blanket cylinder forming a printing nip parallel to the sheet guiding cylinder, the device including at least one sheet guide disposed in a region of the printing nip. The at least one sheet guide has blast openings for guiding a sheet on a shell surface of the sheet guiding cylinder. The blast openings include a combination of free jet nozzles and throttled air blast nozzles.
An advantage of the invention is that the guide device represents a combination of conventional nozzles (free jet nozzlesxe2x80x94with good response behavior even at greater distances of the sheet from the nozzle given large air throughputs), and throttled nozzles (having high air pressure in the near zone of influence given small distances between the nozzles and the sheet and given small air throughputs).
As such, the invention makes it possible to place the guide element with its front part having throttled blast nozzles in front of the infeed nip, e.g., the printing nip, (when viewed in a sheet transport direction), very close to the circumferential surface of the cylinder that transports the sheet. A back part of the guide element includes a number of blast nozzles (in any case, at least one) that already xe2x80x9cpress smoothxe2x80x9d the sheet with their free jet further in front of the infeed nip.
In accordance with another feature of the invention, the at least one sheet guide is at least two sheet guides, one of the two sheet guides is disposed in front of the printing nip with respect to a sheet transport direction, and another of the two sheet guides is disposed behind the printing nip with respect to a sheet transport direction.
In accordance with a further feature of the invention, the throttled air blast nozzles are disposed closer to the sheet guide cylinder than the free jet nozzles.
In accordance with an added feature of the invention, the throttled air blast nozzles are charged with a blasted air pressure at a given pressure level, and the free jet nozzles are separately charged with a blasted air pressure at a pressure level different from the given pressure level.
Advantageously, the throttled nozzles are charged with a higher (approximately 5 times stronger) blasted air pressure than conventional free jet nozzles. It is expedient to dispose an additional sheet guiding device in back of the printing nip, the additional sheet guiding device having, in a region facing the air gap, at least one conventional nozzle (free jet nozzle) for peeling the freshly printed sheet from the inking cylinder, and also having xe2x80x9cthrottled blast nozzlesxe2x80x9d for uniform sheet guidance in a guide region located further from the printing nip.
It is also advantageous to develop the throttled nozzles such that each of the openings is connected to an air-pressure generator through an air throttle. The air throttle can be integrated into the air conducting system at a distance from the respective throttled air nozzle. The air throttle and the air nozzle that is throttled thereby may also form one structural unit in the form of a throttle nozzle. In such a case, a separate air throttle is allocated to each of the throttled air nozzles. But an air throttle can also be provided that is simultaneously pneumatically connected to several throttled air nozzles through the air conducting system.
In accordance with an additional feature of the invention, the throttled air blast nozzles are throttled air nozzles.
In accordance with yet another feature of the invention, there are provided at least one air throttle fluidically connected to the air blast nozzles.
In accordance with yet a further feature of the invention, a fill column is an internal component of the air throttle. The fill elements thereof form flow resistors for the blasted air or suction air that is generated by the air pressure generator and that flows though the air throttle.
In accordance with yet an added feature of the invention, the air throttle has a filter piece. Advantageously, an air-filter-type throttle piece is an internal component of the air throttle. The throttle piece forms a flow resistor for the suction air or blasted air. For example, the throttle piece may be a textile layer that may or may not be woven. The throttle piece may also be a porous and, therefore, air-permeable sponge formed from a plastic.
In accordance with again another feature of the invention, the air throttle has a spiral air channel.
In accordance with yet an additional feature of the invention, the air throttle contains air barriers that protrude into the flow path of the suction air or blasted air and that define eddy chambers disposed between the air barriers.
In accordance with again a further feature of the invention, the air throttle has perforated plates disposed on top of one another and eddy chambers disposed between the perforated plates.
In accordance with again an added feature of the invention, the air throttle is constructed as a perforated plate maze.
In accordance with again an additional feature of the invention, the throttled air blast nozzles are blast nozzles.
With the objects of the invention in view, there is also provided a sheet-fed rotary press for processing printing material sheets including a form cylinder, a rubber blanket cylinder, a sheet guiding cylinder, the sheet guiding cylinder and one of the form cylinder and the rubber blanket cylinder forming a printing nip parallel to the sheet guiding cylinder, and at least one sheet guide disposed in a region of the printing nip. The sheet guide has blast openings for guiding a sheet on the shell surface and the blast openings include a combination of free jet nozzles and throttled air blast nozzles.
Other features that are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a device for guiding sheets in a sheet processing apparatus, it is, nevertheless, not intended to be limited to the details shown because various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.